In the automobile repairing industry, an automobile is finished by repairing a portion damaged by an accident, or by replacing the damaged part by new one to such a level that the damaged portion cannot be discriminated from the original state.
The parts of the automobile portions to be repaired contain various ones such as bonnets, doors, roofs, front pillars, center pillars, rear fenders, back panels, trunk floors, bumpers, wheel houses, life baffles, battery trays, core supports and bumper beams.
These parts have not only flat portions but also portions of complicated shapes such as curved portions, pressed rough portions and holed portions. For example, the bonnets, the doors and the roofs have many flat portions, but the remaining parts have less flat portions but more complicated portions such as the curved portions, the pressed rough portions and the holed portions.
When the damaged portions having the recessed portions are to be repaired, these recessed portions are repaired by beating and applying putty. The repaired surfaces are coated with a primer surfacer, as called “prasurf” in the art, and then with an over-coating paint. When the damaged parts are replaced by new ones, the parts are also over-coated but may also be coated with the prasurf before the over-coating.
Prior to these coating steps, the surface to be coated is always roughened with abrasive paper or the like, so as to enhance the adhesion of the paint. This roughening treatment is called the “ashitsuke-sanding”, which usually uses the abrasive paper or a nonwoven fabric abrasive. In the case of the roughing-sanding before the prasurf coating, for example, it is a current practice that the flat portions are sanded with the abrasive paper of P240 to P400 whereas the remaining portions such as the curved portions, the pressed rough portions and the holed portions are generally sanded with a nonwoven fabric abrasive equivalent to #320.
In the sanding, the abrasive paper is frequently preferred to the nonwoven fabric abrasive, because the abrasive paper is excellent in grinding property and short in working time.
However, the abrasive paper has poor conformability to the curved shape and a strong touch on the coated film. Thus, there arises a defect that a coated film separation is easily caused by an irregular sanding or an excessive sanding, when the curved portions, the pressed rough portions and the holed portions are sanded.
On the other hand, the nonwoven fabric abrasive is inferior in the grinding property and the working time to the abrasive paper, but has a suitable cushion and conforms easily to the shape of the object to be ground. Thus, the nonwoven fabric abrasive is frequently employed, when the complicated faces having the curved portions, the pressed rough portions and the holed portions are sanded.
However, the nonwoven fabric abrasive is inferior in a cutting power to a dry-sanding abrasive paper. Therefore, it is ordinary that the nonwoven fabric abrasive takes a long time for the sanding work and cannot keep the cutting power for a long time. Moreover, the nonwoven fabric abrasive has a low cutting power, and the user is required to work with all his or her strength. The user gets tired and finds it difficult to sand homogeneously and uniformly. Still moreover, the sanding with the nonwoven fabric abrasive has problems that it has a partially deep flaw easily and a sanding trace at a subsequent step.
Thus, the sanding with the nonwoven fabric abrasive has the various problems. For the complicated faces having the curved portions, the pressed rough portions and the holed portions, however, no abrasive article can have replaced the nonwoven fabric abrasive. Thus, it is the current practice that the nonwoven fabric abrasive has been continuously used for a long time.
Japanese Patent Laid-Open No. Hei. 9-123065 has disclosed an abrasive sheet which is used for adjusting the skin of a painted surface so that it is suited for repairing an automobile.
This abrasive sheet has an adhesive layer sandwiched between a flexible resin film and a flexible resin. Therefore, this abrasive sheet is so flexible that it can conform to and sand a very fine orange peel of several microns formed by painting.
However, this abrasive sheet was used to perform the roughing-sanding on a surface of a complicated shape to be repaired. The abrasive sheet could conform well to and sand the complicated surface to be repaired. However, it has been found that the abrasive sheet was so flexible that it caught and broke the complicated surface.
Patent Document 1: Japanese Patent Laid-Open No. Hei. 9-123065